10.5" or 11.5" barrel for carbine gas system?

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Ryanxia

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I researched this quite a while back and don't remember what the general consensus was (if there was one).

Is there an optimal barrel length between 10.5" or 11.5" barrel when using a carbine length gas system?

I know either will shoot fine, and I'll be using an adjustable gas block I'm just curious if anyone knows if there is a noticeable different between recoil impulse / smoothness in shooting? I know pressures change a decent amount the further/closer the muzzle is from the gas port, I just don't remember which direction.

Thanks for any input.
 
I saw you just posted this. I was looking for something else, but I’ll stop and give you my two cents...

I have a BCM 11.5. I’ve shot both a civilian DD MK18 and a Colt 10.3 or 10.5. And whatever the Army had a decade ago Colt Commando or maybe it was a MK18.

From everything I’ve read, BCM and some Colts use the 11.5 because it’s optimal.

I cannot tell the difference in shooting any of them between the 10.5 and 11.5. All have the same recoil and big blast. That was with a range of ammo. 55fmj to 77otm.

I know is my 11.5 is 100% reliable. And my friends with other SBRs say the same about theirs - DD and Colt.

Your adjustable gas block may solve any of problems associated with short carbine barrels.
 
Thanks Wisco. I have a couple of 10.5" SBR's but I'm building another one to make my 'primary' rifle and just not sure if 11.5" would be better, I seem to recall that it was slightly better. Never had any issues with my other ones but might as well try to squeeze as much as I can out of it if I have the option when buying.
 
No problem.

There’s something about dwell time that I don’t quite fully understand that supposedly has to do with 11.5 being better, but maybe that’s negated by a larger gas port?

I’m the opposite of you and looking at the 10.3 for my next upper because I feel like another inch is getting more of my money’s worth of the $200 tax stamp:)
 
That's part of the reason I'm asking, I don't want to add an extra inch for no reason. :D

But I have a 6.5" AR that I can play with if I want to go really short. :)
 
The difference is pretty negligible, although shorter dwell time is going to work better suppressed. Not that it matters if you're running an adjustable GB.
 
The difference is pretty negligible, although shorter dwell time is going to work better suppressed. Not that it matters if you're running an adjustable GB.

Adjustable gas block aside, the shorter barrel is the shorter dwell time?
 
I've heard repeatedly that 11.5 inch is more reliable, but I was never sure if that was people just regurgitating internet lore or what.

That being said I have a 10.5 inch and it's been pretty reliable (one stuck steel case after mixing brass and steel cased ammo in a really dirty gun out of perhaps 5k rds).
 
Didn't the military use 11.5" because of minimum energy/velocity requirements, not because of any reliability concerns?
 
I cant notice a difference in 10.5 or 11.5 carbine length OR 11.5 with mid length gas (Faxon Big Gunner). They all feel the same with adjustable gas blocks. The real difference is downrange. That extra inch gains you a pretty significant boost in ballistics.
 
I have an 11.5 and it runs great. Not very scientific, I know....

But if you're doing a pistol, the 11.5" puts it at the overall length to run a VFG... I think. I dont run one, but I think that's why I went with the extra inch. Sorry if that's a derail. And someone please correct me if I'm wrong.
 
I have an 11.5 and it runs great. Not very scientific, I know....

But if you're doing a pistol, the 11.5" puts it at the overall length to run a VFG... I think. I dont run one, but I think that's why I went with the extra inch. Sorry if that's a derail. And someone please correct me if I'm wrong.

You can make 26" OAL with an 8.5" barrel
 
No pistols, I do SBR's. Thanks for all of the input. My main interest was in the smoothness but as some have stated it won't make a noticeable difference with an adjustable gas block. I'll just have to decide if I want the extra inch for the ballistics but probably I'll stick with another 10.5" since I will be running a suppressor on it as well and want to keep the length down.
 
I've used both the 10.5" and 11.5" barrel fitted with an adjustable gas block, with and without suppressors. The main difference I've noticed between the two is drop and energy at three hundred yards. The 11.5" barrel has a noticeable edge.

The biggest difference in smoothness and soft recoil came with choosing a buffer and recoil spring. I tried the carbine, H and H2 buffers with a standard carbine spring. The H2 buffer felt the softest of the three.

What felt even softer was the A5 RE, A5H2 buffer and the Sprinco green action spring.

My favorite combination is the 11.5" barrel, SLR adjustable gas block and A5 RE assembly with a suppressor.
 
Carbine gas tube is 7.5 inches long. You need barrel length from that gas port forward to hold pressure on the system to operate the action. Either length should be fine, especially if a suppressor is used. Just gotta make sure you have pressure high enough and for long enough to cycle the action.
 
I prefer a 11.5" with heavy profile. We had 10.5" at work, and I used a 11.5" on one deployment. I think the extra length and weight up front is an advantage when firing fast.
 
I've used both the 10.5" and 11.5" barrel fitted with an adjustable gas block, with and without suppressors. The main difference I've noticed between the two is drop and energy at three hundred yards. The 11.5" barrel has a noticeable edge.

The biggest difference in smoothness and soft recoil came with choosing a buffer and recoil spring. I tried the carbine, H and H2 buffers with a standard carbine spring. The H2 buffer felt the softest of the three.

What felt even softer was the A5 RE, A5H2 buffer and the Sprinco green action spring.

My favorite combination is the 11.5" barrel, SLR adjustable gas block and A5 RE assembly with a suppressor.

That's some really good input. Thanks a lot for sharing. And thanks to everyone else as well.
 
I'm also thinking of doing some more research on the adjustable bolt carrier groups that are out. Gemtech makes one with a suppressed and unsuppressed setting and Bootleg makes one with 4 positions although it lacks notches for forward assist.
 
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